DSL communications use copper telephone lines (e.g., twisted pair) for high-speed data transmission. A major problem for DSL service providers is to accurately qualify a subscriber's local loop (sometimes referred to as “probing the line”) prior to the deployment of DSL service. Using line probing techniques, operators can identify and locate any blocking elements that disqualify the loop for DSL deployment and determine whether DSL service can be provided on the loop.
If the loop is qualified, then line probing techniques can be used to determine the type of DSL service through identifying the line topology and noise characteristics. Line probing can also provide guidance as to how to improve the service by removing certain elements from the loop or disturbers from the bundle. This type of probing is provided prior to DSL deployment. After DSL deployment and in the case of a problem interrupting the modem connection, line probing techniques can be used for troubleshooting to identify and locate problems, as well as to provide continued service improvement.
In either case (pre or post DSL deployment), line probing saves the cost and time associated with sending a technician and equipment to the customer cite (sometimes referred to as a “truck roll”). There are generally two types of line probing: Single Ended Line Probing (SELP) and Double-Ended Line Probing (DELP).
SELP is the process of qualifying and/or identifying the loop from the Central Office (CO) end of the loop. The customer premises equipment (CPE) end of the loop may be open or telephone-terminated. Example, single ended line probing techniques are described in U.S. Pat. No. 6,668,041, titled “Single Ended Line Probing in DSL System” and U.S. Pat. No. 6,801,601, titled “Single Ended Line Probing in DSL System Using Transformerless Hybrid.” Each of these patents is herein incorporated by reference in its entirety.
With DELP, on the other hand, both the CO and CPE are involved in the line probing process. One known DELP technique compares information collected at the CPE with a channel and remote terminal simulation model at the CO. By matching the collected data and the model-generated data and through an exhaustive search, it is possible to identify the exact loop configuration. However, such matching techniques employ algorithms with complex mathematical structure that have poor performance when fed with real data (corrupted by measurement error). Moreover, an exhaustive search of this type for matching modeled data to collected data is not time-efficient, and its long execution time makes it impractical.
What is needed, therefore, are double-ended line probing techniques that are time-efficient and less sensitive to measurement errors.